Update the test suite names for ReviewRequestManager tests.

DbQueryTests had tests named after the old DB query functions we had way
back before introducing ReviewRequestManager. The names and docstrings
were old and outdated. This updates them for the appropriate names,
making it easier to see if they fail, and to introduce new tests.
Backport the new testing app.

This transitions the new testing app on master to older releases. This
contains utilities for making it easier to write new unit tests without
the need of slow-to-load fixtures, and adds fixture caching.